Several areas of investigation will be pursued concurrently. The cellular basis of desensitization will be investigated in mice by attempting to identify the key subset of lymphocytes capable of transferring the capacity for non-specific sensitization from a donor to a recipient animal. The factor or factors produced by such desensitized cells when exposed to antigen in vitro which are capable of transferring the capability of densensitizationto recipients will be purified, identified and compared to known lymphokines. In guinea pigs we propose to compare densensitization with antigenic competition with reference to the subsets of lymphocytes regulating these events. We will use cyclophosphamide as a probe to ablate subsets of lymphocytes required for regulation while retaining effector lymphocytes necessary for the delayed-type skin reaction. Experiments involved in the elucidation of the mechanism of cutaneous basophil hypersensitivity will concentrate on the identification and isolation of serum factors obtained from delayed-type hypersensitive animals immunized with complete Freund's adjuvant which when transferred in concert with lymphoid cells will reproducibly transfer DTH and suppress CBH in recipient aimals. The nature of this CBH suppressor factor will be characterized and elucidated.